Videoconferencing service provides distance multimedia service including video, audio and data. With videoconferencing service, when people communicates with each other in different places, voices of the participants can be heard and their images can be seen; thus the communication fills with feeling of reality, closeness and on location. Videoconferencing service can be used in military, politic, economic, education and health fields; the advantages of reality, high efficiency and real-time will give people an effective manner for communication, management and collaborative decision-making.
The videoconferencing service is a communication mean which is used for having a meeting among two or several places through transmission channel by means of video technology and devices. As shown in FIG. 1, in general, a videoconferencing system includes videoconferencing terminals, transmission channels and multi-point control units (MCUs); they will be described in the following.
A videoconferencing terminal is directly operated by the subscriber and provides input and output of video, audio and data signals to the videoconferencing system; a videoconferencing terminal includes a video input/output device, an audio input/output device, a terminal processor and a terminal management system, and optionally includes peripherals such as a power amplifier device, a big screen or an electronic white board etc.
A videoconferencing terminal, on the one hand, samples, compresses, codes and multiplexes the video, audio and data signals at the videoconference site in real time, and then transmits to a transmission channel; on the other hand, classifies, decodes and recovers the received signal to the original video, audio and data signals. Besides, a videoconferencing terminal also transmits control signals of the videoconference at local site, such as request to speak, request the videoconference control claim etc., to the MCU, and executes commands sent by the MCU.
As shown in FIG. 1, in the present technology the MCU is the control kernel of a videoconferencing system. When a videoconference has more than two participants, i.e. two videoconferencing terminals, it must be controlled by a MCU, and all videoconferencing terminals are connected to the MCU with standard interface; the MCU implements exchange and mixture of the video and audio signals according to the international standard protocols, such as H.221, H.242, H.243 and T.120. In general, a MCU is consisted of two parts: a central processing unit and a console; the central processing unit implements functions specified in the protocols and the console implements a man-machine interface where the operator sends commands and operations to the MCU; when the videoconferencing service is opened to the public, a service room is needed to implement videoconference registration, reservation and billing etc.
In a videoconferencing system, it is necessary that there is a communication network to connect videoconferencing terminals and MCUs; physically, these transmission channels may be a fiber, a cable, a microwave mode or a satellite mode. Usually communication networks for a videoconferencing system are: the Public Switched Telephone Network (PSTN), the Packet Switched Public Data Network (PSPDN) and the Digital Data Network (DDN) etc.; at present with the ATM technology, some broadband networks, such as B-ISDN, IP network and IQ network may be used for videoconferencing service. Along with popularization of the ISDN and Internet network, application of the videoconferencing service is spread.
Nevertheless, the present videoconferencing system lacks effective management mechanism on great capability, thereby the capability of the MCU cannot be extended on the great scale; they can be only used for a small number of services so that utilization efficiency of the network is low. In this case, it is difficult to open videoconferencing service to the public.